fix(treesitter): use vim.highlight.priorities instead of hardcoded 100 (#24052)

Problem: Treesitter highlighting base priority cannot be customized.

Solution: Use `vim.highlight.priorities.treesitter` instead of hard-coded value.

runtime/lua/vim/treesitter/highlighter.lua

@@ -260,12 +260,14 @@ local function on_line_impl(self, buf, line, is_spell_nav)
       local spell_pri_offset = capture_name == 'nospell' and 1 or 0
 
       if hl and end_row >= line and (not is_spell_nav or spell ~= nil) then
+        local priority = (tonumber(metadata.priority) or vim.highlight.priorities.treesitter)
+          + spell_pri_offset
         api.nvim_buf_set_extmark(buf, ns, start_row, start_col, {
           end_line = end_row,
           end_col = end_col,
           hl_group = hl,
           ephemeral = true,
-          priority = (tonumber(metadata.priority) or 100) + spell_pri_offset, -- Low but leaves room below
+          priority = priority,
           conceal = metadata.conceal,
           spell = spell,
         })